This invention relates to a power on/power off control arrangement of a video display.
A liquid crystal display (LCD) or and a liquid crystal on silicon (LCOS) television (TV) receiver projection system often uses a high-intensity discharge lamp, or bulb, as a back lighting source. High intensity discharge lamps operate with mercury vapor. It is known that preventing the mercury vapor from de-energizing before re-striking the vapor (i.e., turning power to the lamp back on immediately after or shortly after turning the power off) may shorten the bulb life. Because re-energizing a partially energized bulb should be avoided, some projection systems introduce a restart delay. The user is prevented from turning the TV receiver back on until the bulb is fully de-energized that occurs, for example, after approximately 30 seconds. This approach is particularly annoying to the user because the user is not able to turn the TV receiver back on immediately, as is possible in a TV receiver that does not use a high-intensity discharge lamp. Instead, the user must endure a start-up delay. The start-up delay includes approximately 30 seconds for the bulb to cool down and approximately another 30 seconds for the bulb to reheat.
In response to a user""s command requesting system turn off, the InFocus model LP755 Front Projector, for example, made by Infocus Corporation, will display a message asking xe2x80x9cDo you really want to turn off the system?xe2x80x9d. This approach gives the user the opportunity to re-consider before shutting down, but does not solve the problem directly. Also, this approach is awkward because at least about 90% of all power-off commands are intentional. It may be desirable to eliminate the restart delay, when the user tries to turn on the receiver immediately after turning it off.
In response to a user power off command, a TV receiver, embodying an inventive feature, will immediately give a false appearance of being turned off. In spite of the turn off appearance, the bulb is maintained powered on or energized, during a first interval of, for example, 30 seconds that immediately follows the power off command.
Should the user issue a power on command, before the first interval has elapsed, the user will not experience any start-up delay. The first interval should be, advantageously, more than long enough to accommodate an inadvertent or unintended power off command. Thus, the user would experience a start-up delay, only when the user issues a power on command, after the first interval has elapsed.
It may be desirable to create in the user, during the first interval, a sufficiently convincing false impression of a powered-off TV receiver that, in other words, will fool the user. One might very well expect that different users will respond to different visual and audio cues when assessing whether or not a power off command has indeed turned off a television receiver, even if the user is not particularly cognizant of such an analysis. The absence of a picture, the absence of sound and the absence of light from the power on indicator can each work alone and/or in combination to fool different users at different times.
In accordance with the inventive arrangements, the TV receiver will appear to be xe2x80x9csomewhatxe2x80x9d convincingly off, during the first interval. The term xe2x80x9csomewhatxe2x80x9d is used because the lighted lamp can not be masked completely. The lamp is generally disposed at the rear of the cabinet and is well shielded to prevent accidental eye damage. However, the lamp is ventilated and cooled and some light will inevitably escape from the cabinet and be perceptible to some extent, especially if the ambient light is dim. Moreover, a cooling fan may continue to operate and noise from the fan might be perceptible as well. Nevertheless, for purposes of creating an illusion for the short period of time in which the TV receiver is likely to be switched back on after being unintentionally turned off, the illusion is sufficiently convincing. It should be remembered, after all, that a magician""s audience is still thrilled by the magician""s tricks even though the audience is well aware that the tricks are illusions.
A video display apparatus, embodying an inventive feature, includes a back lighting lamp that is energized, during a normal video display mode of operation, to produce an image. A source of an input, power-on-control signal is provided. A source of an input, power-off control signal is provided. A first timer is responsive to the power-off control signal and coupled to the lamp for maintaining the lamp energized, during a first interval, that follows the occurrence of the power-off control signal. The lamp is de-energized following an end of the first interval. If the power-on control signal occurs, during the first interval, the lamp is prevented from being de-energized, following the end of the first interval, and the normal video display mode operation resumes.